Controls on the Temperature Sensitivity of Soil Enzymes: A Key Driver of In Situ Enzyme Activity Rates

Abstract

Soil microorganisms are surrounded by organic matter that is rich in carbon and nutrients that are required for growth and cell maintenance. However, microbes cannot directly transport these macromolecules into the cytoplasm. Rather, they rely on the activity of a myriad of enzymes that they produce and release into their environment. These enzymes depolymerize organic compounds and generate solu- ble oligomers and monomers that are then recognized by cell wall receptors and transported across the outer membrane and into the cell. Thus, the activities of extracellular enzymes are critical to soil functioning and for maintenance of the vast biodiversity of organisms in soils. The activity of glucosidases, phosphatases, phenol oxidases, and other enzymes that degrade the principal components of detrital organic matter have been exten- sively studied from many perspectives. In early studies, the physical and kinetic characteristics of soil enzymes were a major topic (Bremner and Zatua 1975; McClaugherty and Linkins 1990; Frankenberger and Tabatabai 1991b). More recent studies have concentrated on the ecological significance of soil enzyme activity as a mediator of nutrient cycling. Yet, the fundamental role of temperature in regulating enzyme activities under field conditions has been examined in rela- tively few studies. In theory, the temperature sensitivity of enzyme activities can be described from first principles of thermodynamics. In this chapter, we consider the utility and limitations of thermodynamic extracellular enzyme activity models for understanding the dynamics of ecosystem processes, and we review our current understanding of the thermal ecology of extracellular enzymes in soils.